1. Field of the Invention
The present invention relates to a method of measuring crosstalk noise in a playback information signal and in particular to a method of measuring crosstalk noise in a playback information signal derived from a recording disk such as a video disk.
2. Background Information
Generally, each track of a recording disk such as a video disk has recorded thereon one frame (corresponding to one display picture) of a video signal. Crosstalk noises arise from transfer into a desired playback signal (i.e. obtained from a disk recording track which is currently being played) of interfering signals resulting from data recorded on tracks immediately adjacent to that which is being played. A prior art method used to observe and measure such crosstalk noises will be described referring to FIGS. 1 (A) to 1(C). Picture data of the form shown in FIGS. 1(A) to 1(C), i.e. three consecutive frames of a video signal, are respectively recorded on three immediately adjacent recording tracks of the disk to measure the crosstalk noises. The data recorded on the central one of these three tracks is repetitively played back, whereby the display image shown in FIG. 1(D) is produced. Beat interference, indicated by the portions enclosed in broken-line outlines, arises as a result of crosstalk. Measurement of such crosstalk noise has been performed in the prior art by rendering the crosstalk level visible on a CRT display in this way.
However, there are basically two forms of generation of such crosstalk noise, i.e. noise produced by an interference component from a bright portion of the desired image being mixed with a dark portion of the desired image, and noise resulting from a component of a dark portion of the image being mixed with a bright portion of the desired image. With the prior art method of crosstalk noise measurement described above, it is not possible to measure both of these types of crosstalk noise at the same time. Furthermore since this prior art measurement method is dependent upon human vision, substantial amounts of measurement error can arise, since measurement accuracy will largely depend upon the experience of the test operator.